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Electric field stress control of Cold Shrinkable Cable Accessories

2022-11-07
Electric stress control refers to the control of electric field distribution and electric field intensity, it can be said that the use of appropriate measures to make the electric field distribution and electric field intensity of the power line and line in the best state, so as to improve the reliability of the overall operation and service life; Due to the distortion of electric field at the cable shield break and the end insulation break, the uneven chaotic electric field has both axial and radial distribution, among which 50%~60% is distributed at the radial shield break. In order to eliminate the influence of the uneven electric field, electrical stress control must be carried out. Without electrical stress control, the terminal life depends on the electrical stress at the end of the shield and the discharge resistance of the main dielectric, and its life is generally not more than one year. In order to improve the electrical stress distribution at the cut-off point of cable insulation shielding layer, cold shrinkable cable accessories are generally adopted:

1. Geometric shape method: Stress cone is used to alleviate the concentration of electric field stress (i.e. the increase of curvature radius).

2. Integrated control method: Capacitance cone is used to alleviate the concentration of electric field stress.

3. Parameter control method: The use of high dielectric constant material resistance material to relieve the electric field stress concentration, or the use of nonlinear resistance material to relieve the electric field stress concentration.


Cold Shrinkable Termination kit


The stress control of cold shrinkable cable accessories generally adopts the parameter type or geometric shape method, but the parameter type method needs to add a lot of high medium materials in the silicone rubber to reduce the mechanical strength, which is easy to crack or cause layer cracks when expanding, and the quality is more unstable. Now the geometric shape method is used.

The conductive mechanism of liquid semi-conductive silicone rubber is different from that of conductors and insulators. It is generated by the way that electrons jump from a carbon black polymer to a carbon black aggregation through the polymer. The overall structure of the cross-linked cable has a conductor shield (inner conductive layer) and an insulation shield (outer conductive layer), so the cold-shrinkable cable accessories need semi-conductive silicone rubber. According to the theoretical basis of the resistivity limit of the semi-conductive shield, the voltage assigned to the semi-conductive shield is 1/1000th of the insulating layer, which is quite safe and will not cause the breakdown of the insulation layer. Therefore, in general, to ensure the safe operation of the cable, the resistivity of the semi-conductive layer is required to be less than or equal to 105Ω cm. 

However, the semi-conductive shielding layer of cold shrinkable cable accessories has a 20%~30% restricted shrinkage on the cable body after expansion (stretch). Due to the expansion (stretch) of 20%~30%, the carbon spacing of the semi-conductive shielding increases, which inevitably leads to the increase of the volume resistivity of the semi-conductive shielding. The resistivity must be ≤ 100 ~3Ω cm to meet the standard requirements.

Cold Shrinkable Termination kit

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